This invention relates in general to rotating disk abraders and, more specifically, to such abraders using a square or polygonal pad and having a more effective abrading dust removal system.
High speed disk abraders, which also may be used for grinding and polishing, are the fastest abrasive material removal hand tool available. They are not used for fine finishing or precision bulk material removal because of the poor finishes produced by the usual round abrasive pads. Slower abrasive tools such as belt sanders, orbital or vibrating finish sanders or large floor mounted machinery must be used to achieve a fine, even, finished surface.
A round backup pad with a corresponding round abrasive sheet is used in rotating abrasive machines. Typical of these machines is that described by Hutchins in U.S. Pat. No. 4,145,848. This arrangements has a very aggressive abrading/cutting surface at the outer, circular, edge of the abrasive sheet. The operator normally uses the feel of the outer portions of the rotating pad to stabilize the position of the abrasive sheet relative to the surface being abraded. Because of the greater amount of abrasive near the outer edge of the circular-sheet relative to areas near the sheet center and the extremely high rim speeds of the outer edge of the sheet, combined with the fine line around the outer edge of the abrading sheet, slightly tilting the pad quickly and easily cuts gouges and uneven surfaces into the work. As the pad is moved across a surface being abraded, which may be flat or convex, it is very difficult to hold the pad and sheet perfectly even with the surface bing abraded.
An additional problem with high speed rotating abrading tools is the large quantity of dust produced. Current systems couple an external vacuum and collection system to a shroud covering the back side and edges of the backup pad holding the abrading sheet. Many combine holes through the abrading sheet and backup pad, communicating with a vacuum shroud covering the back of the backup pad. Besides the expense and awkwardness of having to use an external vacuum and collection system with a hand held sander, the current systems tend to be inefficient for several reasons. Centrifugal forces tend to throw dust toward and beyond the outer edge of the abrading sheet, with the outer, high speed, portion of the sheet doing the major part of the material removal. Holes through the abrading sheet can, at best, capture dust produced axially of the holes. Further, since the abrading sheet is pressed tightly against the workpiece surface during abrading, there is little room for dust or the necessary volume of air to move along the surface to the holes.
In some cases spiral grooves are provided in the backup pad, such as are shown by Hempl et al. in U.S. Pat. No. 5,105,585 to attempt to capture additional dust and direct it to extraction holes through the pad. Only a small portion of the exiting dust is captured, since much exits between grooves and is moving at high speed away from the vacuum extraction direction.
In an attempt to capture dust abraded from the surface at the abrading disk edges vacuum shrouds have been designed that cover the entire back of the backup pad and extend well beyond the edges of the pad. While these shrouds are fairly effective, some problems remain.
Abrading dust is propelled by centrifugal forces outwardly of the pad at high speed and must reverse direction in a very short distance to move back over the top of the pad to the vacuum coupling. Some dust will escape, particularly where grinding or abrading high density materials, such as metals. These large shrouds also limit the operator's visibility of the working portion of the tool and of the workpiece surface where the abrading is being done.
A fully enclosed abrading disk cannot be brought close enough to an upstanding second surface to abrade close to it. The weight, size, visibility and abrading limitations of these shrouds tends to discourage their use. In some cases, a section of the shroud is cut away to allow part of the backup pad to extend beyond the shroud. While this allows close approach to an upstanding surface, the limited cut out often makes maneuvering the tool difficult and severely limits the effectiveness of the vacuum system. Further, when sanding the edge of a surface such as a table top edge, much of the vacuum is in effect lost when the shroud extends over the edge.
While most rotary abraders use circular abrading disks, for a few specialized purposes narrow strips of abrasive material in a crossed configuration are used, such as are described by Duckworth in U.S. Pat. No. 5,403,231 for use in fairing the complex curves of boat hulls and the like. Also, so-called "star" heads having a plurality of narrow strips extending radially from a center hub. These are effective with complex curved surfaces, deburring edges and the like but are relatively ineffective in abrading plane or simple convex surfaces. Further, since the width of the strips are substantially uniform over their lengths, they suffer from the problems of higher abrasion speed along the outer edge discussed above.
Manufacture of round or star-shaped abrading sheets is uneconomical, since there is much wasted material when such shapes are cut or punched from a large sheet of abrading material. Also, more complex equipment is required for cutting such shapes than would be the case with simple, square shapes.
Thus, there is a continuing need for improved rotary abrading systems which more effectively and completely remove abrading dust from the abraded area, simplify and localize the vacuum/collection system, avoid gouges or uneven surfaces caused by slight tilting of the abrading sheet in use, provide a more uniform abraded surface, use more easily and economically manufactured abrading sheets.